This section in the Run tab contains a list of deployed contracts to interact with through autogenerated UI of the deployed contract (also called udapp).

Several cases apply:

The called function is declared as constant or pure in Solidity. The action has a blue background, clicking it does not
create a new transaction. Clicking it is not necessary because there are not state changes - but it will update the return
value of the function.

The called function has no special keywords. The action has a
light red background, clicking on does create a new transaction.
But this transaction cannot accept any amount of Ether.

The called function is declared as payable in Solidity. The
action has a red background, clicking it does create a new
transaction and this transaction can accept value.